Investigators said Nehemiah Griego, 15, had hoped to go on a killing spree and die in a shootout with police.

A Bernalillo County grand jury also indicted Griego on Monday on three counts of intentionally caused child abuse and three counts of death of a child under 12, charges that relate to the killing of his two sisters and brother. Griego is being charged as an adult, prosecutors announced.

Griego told investigators he hoped to end his spree "at a Walmart, with mass destruction," Bernalillo County Sheriff Dan Houston said.

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He said he was "frustrated with his mother," but "he did not articulate that to our investigators any further or give any explanation of that at all," Houston said.

He was arrested the night of January 19 after deputies found the bodies of his mother, father, brother and two sisters in their home on the outskirts of Albuquerque. Investigators believe the killings happened early that morning or late the night before.